One of the major drawbacks of conventional high fidelity sound-diffusers, which consist of several frontally oriented loudspeakers, is that high frequencies are radiated in a directional way, i.e. with a reduced angle of emission. This is because sound radiation remains spherical, and therefore omnidirectional, only as long as the radiated wave-length is much greater than the diameter of the sound source, which is generally only true for low frequencies. For example, the wave length of a typical low frequency sound wave is 3.44 m, which is significantly greater than a typical low frequency loudspeaker diameter of 30 cm. Consequently, low frequency sound exhibits a wide emission angle.
However, for increasingly higher frequency sound waves, the wave length decreases, and eventually becomes smaller than the diameter of the source. At this point, nearly the entire wave energy is radiated directionally along the speaker axis. Consequently, the source emits plane waves exhibiting a narrow emission angle.
Consequently, conventional diffusers of this kind, though provided with high-quality parts, have many drawbacks. For example, the response of high frequencies varies considerably throughout the room, and may be too high along the axis giving rise to a squeaky and tiring sound, and considerably attenuated in lateral positions, e.g. 30 degrees off axis. Consequently, the timbres of instruments tend to be distorted, since it is well known that timbres are distinguished by the harmonics of the highest frequency. Another drawback is that the positioning of the diffuser in a common domestic room becomes extremely difficult. Thus, if a highly reflective wall or other object is in the axial path of the diffuser, chain reflections and undesirable echoes occur. If, on the other hand, an absorbing surface is in the axial path of the diffuser, high frequencies are completely absorbed, and the resulting sound tends to be too deep. Another drawback occurs in stereophonic listening, where, in addition to the difficulty of accurately positioning two diffusers, the listening area in which the two stereophonic messages can be heard in their full range of frequencies is rather limited. Out of this narrow area, resulting from the superpositioning of two narrow angles of high frequency radiation, the timbre range of the stereophonic messages is distorted, in that certain positions exhibit an exaggerated stressing of the high-pitched tones of one channel and a damping of the tones of the other channel. Another drawback results from the nature of high fidelity sound reproduction. Thus, reproducing sound in high fidelity means, as far as possible, recreating the atmosphere of the concert hall, where only a small part of the sound reaches the listener directly, the majority being reflected sound. This fact explains and confirms psychoacoustic research which indicates that the human ear tolerates very high levels of reflected sound pressure, and finds lower sound levels unpleasant when sound hits the ear directly.